The present invention relates generally to the field of magnetic tape information storage and retrieval appliances, and more particularly to preventing accumulations from building up on the tape heads of a tape appliance.
Accumulations, including deposits and stain, on the tape heads on a tape appliance that occur during normal use may degrade the performance of the appliance, typically by physically pushing apart the tape medium and the tape heads. This increased distance may lead to an unacceptable degree of spacing loss in the magnetic field strength detected by the read heads, causing a low signal resolution and an unacceptable bit error rate. Spacing loss may be modeled based on the Wallace thickness loss response function, in which the magnetic field strength detected by a read element is proportional to e−kd/λ, where d is the element-to-tape separation, λ is the recording wavelength, and k is a constant equal to 2πf/s, where f=recording frequency, and s=tape speed in recording. Thus, for a given tape generation, the detected magnetic field strength decreases exponentially with respect to separation between the tape and the read element.
The accumulations may be characterized into a few distinct types: predominantly magnetic particle deposits, predominantly polymer deposits, particles from the environment, and stain. The magnetic particle deposits and the polymer deposits are typically loose particles that are shed from one or more layers of the magnetic tape media as it passes over the tape heads. The environmental accumulations are typically airborne particulate contaminants in the tape appliance operating environment that become trapped at the tape head-tape interface. Stain is particles of any type that adhere to the tape head and are difficult to remove, for example, by standard production cleaning tapes or other routine maintenance. Tape stain formation may be an electro-mechanical-chemical process in which an accumulation of lubrication products, head wear products, and other detritus produced from the head and tape builds up on the tape head elements, for example, shields, poles, substrates, reader elements, etc. Accumulations of different types may collect at different locations of a tape head. Because stain typically collects near the pole tips of the tape heads and is difficult to remove, it may disproportionately cause increased head-tape spacing, even though its thickness is only of the order of a few nanometers.
Regular tape head cleaning may remove some or most of the accumulations on the tape head. Typically, at regular intervals, a special cleaning cartridge is mounted in the tape appliance and the tape medium of the cleaning cartridge is moved across the tape heads. The interval may be based on, for example, tape appliance operating hours, number of tape mounts, bit errors occurring above a threshold bit error rate, etc. The cleaning cartridge typically includes an unrecorded tape medium having a surface composition that is more abrasive than the surface of the standard tape medium for the tape appliance. The friction of the cleaning tape medium against the tape heads physically removes the accumulations. Because of the abrasive nature of the tape cleaning cartridge, the frequency of use of the cleaning cartridge should be regulated to not cause excessive wear of the tape heads. Because cleaning cartridges have a useful lifespan of typically around 50 cleaning cycles, the number of cleaning cycles per cleaning cartridge should be tracked. In addition to periodic use of a cleaning cartridge, special procedures may be required to remove accumulated stain on the tape heads. These procedures may include manual cleaning of the tape heads with special solvents.
While frequent use of a cleaning cartridge may reduce the buildup of accumulations on the tape head, especially difficult to remove stain deposits, frequency of use should be balanced against the accelerated wear of the tape heads that will occur with too frequent use of cleaning cartridges.